Solomon Gebreyohannis Gebrehiwot Department of Aquatic Sciences and Assessment, SLU, Box 7050, Uppsala; Kevin Bishop Department of Aquatic Sciences and Assessment, SLU, Box 7050, Uppsala; and Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala Annmieke Gärdenäs Department of Soil and Environment, SLU, Box 7014, Uppsala; Jan Seibert Department of Geography, University of Zurich – Irchel, Winterthurestrasse 190, CH-8057 Zurich, Switzerland; Per-Erik Mellander Research Officer, Agricultural Mini-Catchment Programme, Teagasc, Johnstown Castle Environmental Research Centre, Co. Wexford, Ireland

INTRODUCTION Hydrological change detection Statistical analysis Change detection – modeling Pair watershed approach model parameter changes in a single watershed

Study Site – Blue Nile Basin Koga Gilgel Abbay Birr Upper- Didesa Forest change history Rf ~ 1500 mm Rf ~ 2000 mm Area = 260 (Koga) – 1900 km 2 (Upper-Didesa

Subsistence farming, soil erosion and land use change, seasonal water availability

Snow routine parameters: Model Application - HBV

Periodic classification

METHODS - Change detection Parameter comparison Comparison of the distribution of 50 best parameter sets Using Wilcoxon signed-rank test Residual comparison Using parameter sets from P1 then simulating rainfall in P2 and P3 Then calculating residuals for all 3 periods and comparing them Simulation comparison Parameter sets from P1, P2 and P3 simulated for the driest and wettest years, and compare the simulations

Parameter comparison

FCLPBETAK1K2MAX Birr P P P Upper-Didesa P P Gilgel Abbay P IN 2.24 P IN 2.54 P IN 1.89 Koga P P P Table. Medians of model parameter values with test results. Groups in a column colored red are significantly different at ρ  0.05 with Wilcoxon signed-rank test, and those do not are non-significantly different, “IN” shows that the parameters respective to each watershed were insensitive.

Model residuals comparison Annual medians of relative residuals; filled circles showed significant differences and open ones, non significant. “+” indicates the average medians.

Extreme climate simulation comparison Simulations for the driest and wettest years of the four watersheds with parameter sets from the three periods.

Discussion and conclusion Specific parameters are significantly changing Residuals are significantly changing from the reference period – Period 1 ( )

Discussion and conclusion Though parameters were said significantly changing, the response of the watersheds to flow remains less/no change The masking of parameter changes in simulations Scale issue Parameter compensation The impacts of parameter changes might be seen at smaller scale We recommend analysis of relation of model parameters to specific watershed characteristics in the future

Swedish International Development Agency (SIDA)